1. Field of the Invention
The present invention relates to a tissue metabolism measuring apparatus and particularly to a tissue metabolism measuring apparatus for measuring, in a non-invasive manner, changes in an oxygenated state of hemoglobin or a quantity of blood in an organ or other parts of a human body or an animal body as well as changes in an oxidation-reduction action of cytoplasmic cytochrome.
2. Description of the Prior Art
FIG. 1 is a diagram showing a conventional apparatus for measuring a metabolic action in a body organ. FIGS. 2 and 3 are diagrams showing an optical path of light detected in the conventional measuring apparatus.
The apparatus shown in FIG. 1 is described in Japanese Patent Laying-Open Gazette No. 115232/1982. In this apparatus of FIG. 1, a near infrared light source 1 emits alternately near infrared rays of different wavelengths. Each of those near infrared rays passes through the head 3 of a human body by means of an optical fiber 2 so that a detection system 4 measures intensity of the ray. A controller 5 controls transmitting speeds and order of monochromatic flashes and demodulates a detected optical signal. A feedback controller 6 maintains constant the optical signal detected based on one wavelength by negative feedback control of a detection sensitivity and compensates for a change in transmittance caused by a change in a quantity of blood of the organ detected during a fluoroscoping period. An output control circuit 7 outputs a feedback voltage blood quantity indicating signal simultaneously with reception of reference and measuring signals.
The above described apparatus shown in FIG. 1 applies light of a range of 700 nm to 1300 nm to the head 3 and detects light transmitted through the head 3 so as to observe a change in an oxygenated state of hemoglobin or a quantity of blood in the brain as well as a change in an oxidation-reduction action of cytoplasmic cytochrome. This operation is performed by making use of the fact that deoxygenated hemoglobin has a small peak of about 760 nm with an isosbestic point of hemoglobin of 805 nm being used as a reference wavelength or the fact that an absorber dependent on oxygen of cytochrome aa3 exists in a wavelength range of 700 nm to 1300 nm. In addition, Japanese Patent Laying-Open Gazette No. 72542/1985 describes an optical CT apparatus in which a bonded state between oxygen molecules such as hemoglobin or myoglobin in a body and oxygen of protein can be observed quantitatively in a two-dimensional distribution by utilizing light of the wavelength range and absorbing property thereof in the same manner as described above and oxygen density of cytocondria can be observed in a two-dimensional distribution based on an oxidized and reduced state of cytochrome or the like as a constituent of a respiratory chain.
However, if light of the range of 700 nm to 1300 nm has a higher transmittance through a body than that of light in the visible radiation range and if it is applied to the body whereby the transmitted light thereof is detected, the incident light is immediately scattered and absorbed in the body because the wavelength thereof is short compared with the size of hemoglobin, and it follows that the detected light is only a component of diffused light. This is described for example in "Optical Diffusion in Blood" by C. Johnson in IEEE TRANSACTION ON BIO-MEDICAL ENGINEERING Vol. BME-17 No. 2, 1970, pp. 129-133.
More specifically, as shown in FIG. 2, if light irradiated into the body is detected by a detector 9, the light detected by the detector 9 includes not only light passing through an optical path 10a as a straight line connecting the incident point and the detector 9 but also light scattered or diffused and passing through optical paths 10b and 10c rather than the optical path 10a. Thus, when the transmitted light is detected, the path through which the detected light has passed in the body cannot be specified. For example, the apparatus shown in FIG. 1 only makes it possible to obtain information of the whole region subjected to the measurement or an area corresponding to a considerably wider optical path (shown as the hatched portion in FIG. 3) than the optical path 10a as the straight line connecting the incident point and the detector 9, as shown in FIG. 3. Information of such a wide range is useless for a clinical diagnosis of an organic disturbance such as a disturbance of blood circulation in a body or a condition thereof because the location of the disturbance is an important concern.